Synthetic spectra have been calculated from model hydrostatic stellar
atmospheres using physical parameters (effective temperature,
abundances, etc.) appropriate for Cepheids. Velocity gradients have
been kinematically introduced in order to study their effect on line
profile asymmetries and radial velocity curves. The results are
compared to high resolution observations of $\eta$ Aql.

It is shown that a significant velocity gradient is needed near
the phase of maximum infall velocity to account for observed
line profile asymmetries and velocity differences of absorption
lines from atoms of different ionization and excitation. The
effect of this velocity gradient is to reduce the amplitude of the
pulsation velocity curve at optical depth $\tau = 2/3$ by 20\% and to
decrease the $\gamma$ velocity by 2 km/sec relative to the standard
Barnes-Evans or Baade-Wesselink assumption of a co-moving atmosphere.

Barnes-Evans calculations of $\eta$ Aql have been made taking velocity
gradients into account. The resulting size and distance of $\eta$ Aql
is reduced by about 17\%.